Simple tone control?

ss,

_________________ Is *that* why many boomboxes and home stereos(cheap ones) have a tone knob labeled "Bass< >Treble"?

All I notices with those is that turning it to the left made the sound muffled and to the right made the sound more tinny/hissy. I didn't notice that the bass was being boosted when the knob turned left or that it was being reduced when turned right.

-CC

These pots on the circuit references aren't on a common shaft.

In other words, you can have muffled *and* tinny/hissy! ;-)

Dave

This is the classic Baxandall tone control. There is plenty of material if Googling for 'baxandall'.

--

Tauno Voipio

Thanks! It really helps to know what it's called... ;-)

This page:

says: " This circuit must be driven from a low impedance, so connecting it after the volume control (for example) is a no-no. Ideally, the output of an opamp will be the source, thus ensuring the required low impedance. " The input to this circuit will be the output of a computer's sound card. I don't know if it's an opamp driving the output or not.

What do you suggest to insure driving by low impedance? Add a buffer opamp (gain of 1) at the input of this circuit?

Thanks.

The sound card output will be fine for driving this.

d

"Tauno Voipio"

** It's not actually.

Seems like a ballsed up version with missing resistors that will be become unstable at full treble.

** And like most stuff on hobby web sites it is bunkum.

The "Baxandall" tone control design was published in Wireless World in

952 - it used valves. The network is different to the one in the link above and produces variable turnover at both the high and low ends of the range.

... Phil

A general question:

Should pots used in the audio tone filter circuits be audio (log) taper? Or does this apply only to volume pots?

Thanks.

Linear

d

This circuit, "mechanically" lifted from the tube era into op-amp implementation, has a flaw: If the treble control is set to maximum, then its gain is not limited at

+20dB at 10...20kHz, but keeps rising as far as the gain-bandwidth product of the op-amp allows. Input impedance goes down accordingly. It might result in Hf oscillations in the whole audio chain, even to burning the speakers out if say you leave input unconnected and close to the speaker cable.

To fix the (potential) problem:

- insert 470R in series with the input 4.7uF capacitor or insert 470R between the wiper of the treble control and the inverting input of the op-amp;

- throw a 47pF cap from the op-amp output to the op-amp inverting input.